drm/radeon/kms: use correct reg on fusion when reading back mem config

Signed-off-by: NAlex Deucher <alexdeucher@gmail.com>
Signed-off-by: NDave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/evergreen.c

@@ -2248,7 +2248,10 @@ int evergreen_mc_init(struct radeon_device *rdev)
 
 	/* Get VRAM informations */
 	rdev->mc.vram_is_ddr = true;
-	tmp = RREG32(MC_ARB_RAMCFG);
+	if (rdev->flags & RADEON_IS_IGP)
+		tmp = RREG32(FUS_MC_ARB_RAMCFG);
+	else
+		tmp = RREG32(MC_ARB_RAMCFG);
 	if (tmp & CHANSIZE_OVERRIDE) {
 		chansize = 16;
 	} else if (tmp & CHANSIZE_MASK) {